The present invention relates generally to the manufacturing of metal castings and more particularly to manufacturing castings within sand mold packs.
A traditional casting process for forming metal castings generally employs a mold or die, such as a permanent, metal die or a sand mold, having the exterior features of a desired casting, such as a cylinder head, formed on its interior surfaces. A sand core comprised of sand and a suitable binder material and defining the interior features of the casting is typically placed within the die to further define the features of the casting. Sand cores generally are used to produce contours and interior features within the metal castings, and the removal and reclaiming of the sand materials of the cores from the castings after the casting process is completed is a necessity.
Depending upon the application, the binder for the sand core and/or sand mold may comprise a phenolic resin binder, a phenolic urethane xe2x80x9ccold boxxe2x80x9d binder, or other suitable organic binder material. The die or mold is then filled with a molten metallic alloy, which is allowed to cool to a certain, desired degree to cause the alloy to solidify. After the alloy has solidified into a casting, the casting is then moved to a treatment furnace or furnaces for further processing, including heat-treating, reclamation of the sand from the sand cores, and aging. Heat treating and aging are processes that condition metallic alloys so that they will be provided with different physical characteristics suited for different applications. Heat treating may include processing and/or thermal processing.
Sand molds and/or cores generally are removed from the casting prior to completion of heat treatment. The sand molds and/or cores are typically separated from their castings by one or a combination of means. For example, sand may be chiseled away from the casting or the casting may be physically shaken or vibrated to break-up the sand molds and internal sand cores within the castings and remove the sand. In addition, as the sand molds and castings are passed through a heat treatment and/or thermal sand removal furnace, the organic or thermally degradable binder for the sand molds and cores, generally is broken down or combusted by exposure to the high temperatures for heat treating the castings to a desired metal properties so that the sand from the molds and cores can be removed from the castings and reclaimed, leaving the finished, heat-treated castings. Such furnace systems and methods of heat treating castings are found in U.S. Pat. Nos. 5,957,188, 5,829,509, and 5,439,045, each of which is expressly incorporated herein by reference. Once the sand is removed from the casting, heat treating and aging of the casting generally are completed in subsequent steps.
Technology such as that disclosed in the above mentioned patents is driven, for example, by competition, increasing costs of raw material, energy, labor, waste disposal, and environmental regulations. These factors continue to mandate improvements in the field of heat-treating and reclamation of sand from such metal castings.
The present invention comprises a method and system for enhancing the removal of sand molds from castings formed within sand molds. According to one embodiment of the present invention, the sand molds may be removed from the castings by scoring the molds and applying a force sufficient to cause the mold to fracture and break into pieces. For example, the molds may be fractured by thermal expansion of the castings being heated therein by the application of radiant energy or inductive energy to the molds, or by other applications of force and/or energy. Additionally, a high-pressure fluid may be directed at the exterior walls of the mold to further aid in breaking down the mold. Once the molds are fractured and broken into various pieces they generally are then dislodged from the casting. After the molds have been removed, the castings may be heat treated while the pieces of the sand molds are heated to a temperature sufficient to cause the binder materials thereof to combust for breakdown and reclamation of sand from the molds and cores.
In a further embodiment, the method of dislodging a mold from a casting can include placing one or more explosive charges or organic or thermally degradable materials at one or more selected locations within exterior walls of the mold. The explosive charges are detonated at specific times in the process so as to cause the mold to fracture and break into pieces. The broken pieces may then be dislodged from the casting.
Additionally, score lines may be added to the mold containing the explosive charges or organic or thermally degradable or reactive materials. The score lines are operatively placed in combination with the explosive charge(s) and/or organic or thermally degradable materials in predetermined locations to enhance the breaking down and dislodging of portions of the mold from the casting upon initiation of the explosive charge(s). After the mold has been dislodged, heat treatment of the casting may begin or continue.
An additional embodiment includes a method of dislodging a mold from a casting formed within the casting by stimulating the mold with a high energy pulsation. The mold typically fractures after being stimulated by the high energy pulse and the fractured pieces may then be dislodged from the casting. The high energy pulsation typically includes a shock wave, pressure wave, acoustical wave, or combination thereof produced from either mechanical means, cannons, pressurized gasses and electromechanical means. Additionally, score lines may also be applied to the mold to aid in breaking down and dislodging the mold from the casting.
Various objects, features and advantages of the present invention will become apparent to those skilled in the art upon reading the following specification, when taken in conjunction with the accompanying drawings.